U.S. patent number 6,892,001 [Application Number 10/370,462] was granted by the patent office on 2005-05-10 for optical packet header identifier, optical router incorporating the same therein, and optical routing method using the router.
This patent grant is currently assigned to Laserfront Technologies, Inc.. Invention is credited to Yukio Ogura, Yoshinori Ohta.
United States Patent |
6,892,001 |
Ohta , et al. |
May 10, 2005 |
Optical packet header identifier, optical router incorporating the
same therein, and optical routing method using the router
Abstract
An optical packet header identifier having a simplified
configuration and being superior in reliability, stability, and
economical efficiency, an optical router incorporating the
identifier therein, and a routing method using the optical router
are provided. The optical packet header identifier includes an
optical waveguide, optical focusing elements, and a photo receiver.
Tilted gratings for diffracting an incident optical beam and
emitting the beams as diffracted optical beams to the outside of
the waveguide are formed within the optical waveguide. The tilted
gratings are not formed uniformly in a longitudinal direction of a
core of the optical waveguide, but are arranged at intervals. The
length of a portion containing a set of gratings and the length of
a portion containing no gratings can be defined in increments of
length "L". "L" equals to the spatial length which 1 bit in an
optical signal occupies.
Inventors: |
Ohta; Yoshinori (Tokyo,
JP), Ogura; Yukio (Tokyo, JP) |
Assignee: |
Laserfront Technologies, Inc.
(Kanagawa, JP)
|
Family
ID: |
27750801 |
Appl.
No.: |
10/370,462 |
Filed: |
February 24, 2003 |
Foreign Application Priority Data
|
|
|
|
|
Feb 26, 2002 [JP] |
|
|
2002-049646 |
|
Current U.S.
Class: |
385/37; 359/558;
359/566 |
Current CPC
Class: |
H04B
10/671 (20130101); H04B 10/676 (20130101); H04J
14/0212 (20130101); H04Q 11/0005 (20130101); H04J
14/0227 (20130101); H04Q 11/0066 (20130101); H04Q
2011/0041 (20130101) |
Current International
Class: |
H04J
14/02 (20060101); H04B 10/152 (20060101); H04B
10/158 (20060101); H04Q 11/00 (20060101); G02B
006/34 () |
Field of
Search: |
;359/558,566
;385/37 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lee; John R.
Assistant Examiner: Gurzo; Paul M.
Attorney, Agent or Firm: Young & Thompson
Claims
What is claimed is:
1. An optical packet header identifier for identifying a header of
an optical packet, comprising: an optical waveguide, a tilted
grating for diffracting an optical beam propagating within a core
of said optical waveguide toward an outside of said optical
waveguide, a set of tilted gratings constituted by said tilted
grating and having a thickness of gratings approximately equal to a
length occupied in a direction along an optical axis within said
optical waveguide by one bit of a signal of an optical packet, and
said plurality of sets of tilted gratings are encoded and arranged
in a direction along an optical axis based on a specific header
code for said optical packet; optical beam focusing means for
spatially focusing optical beams diffracted by all of the sets of
tilted gratings; a first photo receiver for receiving said focused
optical beams; and a second photo receiver for receiving an optical
beam propagating through said optical waveguide at an output end of
said optical waveguide.
2. The optical packet header identifier according to claim 1,
wherein said optical waveguide is any one of an optical fiber and a
channel waveguide formed on a planar substrate.
3. The optical packet header identifier according to claim 2,
wherein said optical beam focusing means comprises a second optical
fiber for diffracting said diffracted optical beams to cladding
mode by using tilted gratings formed in a core portion of said
second optical fiber, and wherein said first photo receiver is
provided at an end face of said second optical fiber to receive
said optical beams traveling in cladding mode within said second
optical fiber.
4. The optical packet header identifier according to claim 3,
wherein said optical beam focusing means further comprises a third
optical fiber located between said optical waveguide and said
second optical fiber, for focusing said diffracted optical beams
from said optical waveguide onto a center of said second optical
fiber.
5. The optical packet header identifier according to claim 4,
wherein said optical waveguide is provided on a front side of said
third optical fiber, and positioned apart a distance two times a
focal length of said third optical fiber for focusing from said
third optical fiber, and wherein said second optical fiber is
provided on a rear side of said third optical fiber, and positioned
apart a distance two times a focal length of said third optical
fiber from said third optical fiber.
6. The optical packet header identifier according to claim 4,
further comprising a fourth optical fiber, wherein a center of said
optical waveguide is positioned at a front focal point of said
third optical fiber, wherein a center of said second optical fiber
is positioned at a rear focal point of said fourth optical fiber,
and wherein said third and fourth optical fibers focus diffracted
optical beams from said optical waveguide onto said second optical
fiber.
7. The optical packet header identifier according to claim 2,
wherein said optical beam focusing means comprises a "f.o slashed."
lens provided such that a central axis of said core of said optical
waveguide and a light receiving face of said first photo receiver
have relationship represented by "f.o slashed.", and wherein a tilt
angle of each of said plurality of sets of tilted gratings is
determined such that optical beams diffracted from each of said
plurality of sets of tilted gratings are focused onto said photo
receiver by said "f.o slashed." lens.
8. The optical packet header identifier according to claim 2,
wherein said optical waveguide is provided to form a circle in a
plane, said plane having said tilted grating tilted therein, and
wherein said optical beam focusing means comprises: an optical
fiber acting as a cylindrical lens and provided such that said
optical fiber forms another circle around the same center as that
of said circle in the same plane as that for said optical waveguide
to form said circle and a center of said core of said optical
waveguide is positioned at a front focal point of said optical
fiber; a lens for focusing optical beams transmitted from said
optical fiber onto said first photo receiver.
9. The optical packet header identifier according to claim 2,
wherein light-diffracting efficiency of each of said plurality of
sets of tilted gratings is determined such that intensity of
diffracted optical beams from all of said plurality of sets of
tilted gratings becomes uniform.
10. The optical packet header identifier according to claim 1,
wherein said optical beam focusing means comprises a slab waveguide
provided to guide said diffracted optical beams and having a
parabolic reflecting end face for reflecting said guided optical
beams, and said first photo receiver is provided at a focal point
of said slab waveguide.
11. The optical packet header identifier according to claim 1,
wherein said optical waveguide comprises a semiconductor optical
waveguide, and wherein said tilted grating comprises a spatial
periodic refractive index variation generated in said core by a
band-filling effect, said effect being caused when carriers are
injected into said semiconductor optical waveguide, and wherein
said set of tilted gratings is formed by conducting current between
grid-shaped electrodes which is provided on a cladding of said
semiconductor optical waveguide and which is electrically connected
to teach other and an electrode which is provided to face said
grid-shaped electrodes via said semiconductor optical waveguide in
order to inject carriers into said semiconductor optical
waveguide.
12. The optical packet header identifier according to claim 11,
wherein the encoding of said plurality of sets of tilted gratings
is determined depending on whether or not current is conducted to
said grid-shaped electrodes provided along an optical axis.
13. The optical packet header identifier according to claim 12,
wherein said optical beam focusing means comprises a "f.o slashed."
lens provided such that a central axis of said core of said optical
waveguide and a light receiving face of said first photo receiver
have relationship represented by "f.o slashed.", and wherein a tilt
angle of each of said plurality of sets of tilted gratings is
determined such that diffracted optical beams diffracted by each of
said plurality of Bets of tilted gratings are focused onto said
first photo receiver by said "f.o slashed." lens.
14. The optical packet header identifier according to claim 12,
wherein light-diffracting efficiency of each of said plurality of
sets of tilted gratings is determined such that intensity of
diffracted optical beams from all of said plurality of sets of
tilted gratings becomes uniform by controlling current supplied to
each of said plurality of grid-shaped electrodes.
15. The optical packet header identifier according to claim 11,
wherein said optical beam focusing means comprises a slab waveguide
provided to guide said diffracted optical beams and having a
parbolic reflecting end face for reflecting said guided optical
beams, and wherein said first photo receiver is provided at a focal
point of said slab waveguide.
16. The optical packet header identifier according to claim 11,
wherein said optical beam focusing means comprises a second optical
fiber for diffracting said diffracted optical beams to cladding
mode by using tilted gratings formed in a core portion of said
second optical fiber, and wherein said first photo receiver is
provided at an end face of said second optical fiber to receive
said optical beams traveling in cladding mode within said second
optical fiber.
17. The optical packet header identifier according to claim 16,
wherein said optical beam focusing means further comprises a third
optical fiber located between said optical waveguide and said
second optical fiber, for focusing said diffracted optical beams
from said optical waveguide onto a center of said second optical
fiber.
18. The optical packet header identifier according to claim 17,
wherein said optical waveguide is provided on a front side of said
third optical fiber, and positioned apart a distance two times a
focal length of said third optical fiber for focusing, from said
third optical fiber, and wherein said second optical fiber is
provided on a rear side of said third optical fiber and positioned
apart a distance two times a focal length of said third optical
fiber from said third optical fiber.
19. The optical packet header identifier according to claim 17,
further comprising a fourth optical fiber, wherein a center of said
optical waveguide is positioned at a front focal point of said
third optical fiber, and wherein a center of said second optical
fiber is positioned at a rear focal point of said fourth optical
fiber, and wherein said third and fourth optical fibers focus
diffracted optical beams from said optical waveguide onto said
second optical fiber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical packet header
identifier for verifying whether or not an optical address code
added to an optical packet signal transmitted from outside
coincides with an address code previously given to an optical
packet receiver without photoelectric conversion while maintaining
the added code in the form of light and for outputting a result of
the coincidence of codes as an electrical signal output in the
event the two codes coincide with one another, an optical router
incorporating the identifier therein, and an optical routing method
using the optical router.
2. Description of the Related Prior Art
Advent of the Internet community has been drastically increasing
communication traffic. Therefore, there is a demand for realization
of a network that is able to accept the increase in communication
traffic, have a high-capacity, operate at higher rate, and have at
lower communication cost. Optical fiber communication technology is
very the one that meets such requirements.
When focusing attention on the field of communication protocol, a
connectionless communication typified by Internet Protocol (IP) is
becoming increasingly dominant over a circuit switching connection
typified by a telephone network. To achieve a high-capacity and
high-speed communication system of the type used for connectionless
communication, it is desirable to be able to perform optical signal
transmission throughout from a transmitting terminal to a receiving
terminal without any photoelectric conversion.
Routing is a technique for selecting an optimal path to be used
from a plurality of communication paths in order to transmit an IP
packet to a final destination. In an optical communication system,
a wavelength routing system that employs a wavelength as address
information to determine the destination of signal light has been
known as a routing technique that uses an optical signal as it is.
However, this routing technique can be applied only to a
high-speed/capacity portion of communication network because a
wavelength resource, i. e., the number of wavelengths to be
allocated to individual addresses is limited. Currently, it is
difficult to deliver an IP packet to an access path that needs a
number of addresses while maintaining the packet in the form of
light.
A technique using an optically encoding/decoding device for
encoding a light signal, and in turn, decoding the encoded light
signal is disclosed in Japanese Patent Application Laid-open No.
2001-177565.
FIG. 1 is the exemplary configuration of an optical encoder (note
that the optical encoder can be used not only for encoding a light
signal but for decoding the same) composed of 8-tip optical bipolar
encoder of the type used in PLC (Planar Lightwave Circuit) in the
above-described patent. A light pulse input to the optical encoder
is branched into eight tip pulses that are made to have a time
delay of 5 ps between adjacent pulses and equal intensity by
operating a tunable optical tap 41 and an optical delay line 42.
Each of the branched tip pulses is processed such that a phase
shift "0" or ".pi." due to a thermal-optical effect by an optical
phase shifter 43 is given to the optical phase of the tip pulse
,and then encoded by again combining the tip pulses together
through a combiner 44. The given combination of phase shifts thus
corresponds to one code. Each of the optical phase shifters 43 is
controlled in response to an address code, thereby producing a
desired optical bipolar code. In turn, when the optical bipolar
code is input to the same optical encoder, a correlation between
the optical code input thereto and the combination of phase shifts
of the optical phase shifter is detected. A correlation signal
having high intensity is output only when the optical code input
thereto and the combination of phase shifts of the optical phase
shifter coincide with one another, whereby the code is
identified.
In the above-described optical encoder employed in the disclosed
technique, since encoding or decoding is performed by giving a
phase shift "0" or ".pi." to an electric field of light, the
encoding or decoding is so sensitive to change in optical
frequency. Furthermore, the optical encoder is not practical for
use because it has no compatibility with the current optical fiber
communication system in which data or address is
transmitted/received by modulating the intensity of light.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described
problems, and an object of the present invention is therefore to
provide: an optical packet header identifier, without calculation
of correlation in an electronic circuit, having a low power
consumption, operating at higher rate, having a simplified
configuration, and having a superiority in reliability, stability
and economical efficiency; an optical router incorporating the
identifier therein; and a routing method using the router.
An optical packet header identifier according to the first aspect
of the present invention comprises: an optical waveguide, a tilted
grating for diffracting an optical beam propagating within a core
of the optical waveguide toward the outside of the optical
waveguide; and a set of tilted gratings constituted by the tilted
grating and having a thickness of gratings approximately equal to
the length occupied in a direction along an optical axis within the
optical waveguide by 1-bit in a signal of an optical packet, the
plurality of sets of tilted gratings being encoded and arranged in
a direction along an optical axis based on a specific header code
of the optical packet; optical beam focusing means for spatially
focusing optical beams diffracted by all of the sets of tilted
gratings; a first photo receiver for receiving the focused optical
beams; and a second photo receiver for receiving an optical beam
propagating though the optical waveguide at an output end of the
optical waveguide.
The identifier is further constructed such that the optical
waveguide is any one of an optical fiber and a channel waveguide
formed on a planar substrate.
The identifier is further constructed such that the optical beam
focusing means is a slab waveguide provided to guide the diffracted
optical beams and having a parabolic reflecting end face for
reflecting the guided optical beams, and the first photo receiver
is provided at a focal point of the slab waveguide.
The identifier is further constructed such that the optical beam
focusing means comprises a second optical fiber for diffracting the
diffracted optical beams to make the optical beams travel in
cladding mode by using tilted gratings formed in a core portion of
the second optical fiber, and the first photo receiver is provided
at an end face of the second optical fiber to receive the optical
beams traveling in cladding mode within the second optical
fiber.
The identifier is further constructed such that the optical beam
focusing means further comprises a third optical fiber which is
located between the optical waveguide and the second optical fiber,
and focuses the diffracted optical beams from the optical waveguide
onto a center of the second optical fiber.
The identifier is further constructed such that the optical
waveguide is provided on a front side of the third optical fiber
and positioned apart a distance two times a focal length of the
third optical fiber for focusing, from the third optical fiber, and
the second optical fiber is provided on a rear side of the third
optical fiber and positioned apart a distance two times a focal
length of the third optical fiber from the third optical fiber.
The identifier further comprises a fourth optical fiber in addition
to the third optical fiber, in which a center of the optical
waveguide is positioned at a front focal point of the third optical
fiber and a center of the second optical fiber is positioned at a
rear focal point of the fourth optical fiber, and the third and
fourth optical fibers focus diffracted optical beams from the
optical waveguide onto the second optical fiber.
The identifier is further constructed such that the optical beam
focusing means is a "f.theta." lens provided so that a central axis
of the core of the optical waveguide and a light receiving face of
the first photo receiver have relationship represented by
"f.theta.", and a tilt angle of each of the plurality of sets of
tilted gratings is determined so that a diffraction direction
associated with diffracted optical beams from each of the plurality
of sets of tilted gratings satisfies relationship represented by
"f.theta.".
The identifier is further constructed such that the optical
waveguide is provided to form a circle in a plane, the plane having
the tilted grating tilted therein, and the optical beam focusing
means comprises: an optical fiber acting as a cylindrical lens and
provided so that the optical fiber forms another circle around the
same center as that of the circle in the same plane as that for the
optical waveguide to form the circle, and a center of the core of
the optical waveguide is positioned at a front focal point of the
optical fiber; and a lens for focusing diffracted images,
transmitted from the optical fiber and formed in the center of the
circle, onto the first photo receiver.
The identifier is further constructed such that light-diffracting
efficiency of each of the plurality of sets of tilted gratings is
determined so that intensity of diffracted optical beams from all
of the plurality of sets of tilted gratings becomes uniform.
The optical packet header identifier according to the first aspect
of the present invention is further characterized in that the
optical waveguide is a semiconductor optical waveguide, the tilted
grating has a spatial periodic refractive index variation generated
in the core by a band-filling effect, the effect being caused when
carriers are injected into the semiconductor optical waveguide, and
the set of tilted gratings is formed by conducting current between
grid-shaped electrodes which is provided on a cladding of the
semiconductor optical waveguide and which is electrically connected
to each other and an electrode which is provided to face the
grid-shaped electrodes via the semiconductor optical waveguide in
order to inject carriers into the semiconductor optical
waveguide.
The identifier is further constructed such that the encoding of the
plurality of sets of tilted gratings is determined depending on
whether or not current is conducted to a plurality of the
grid-shaped electrodes provided along an optical axis.
The identifier is further constructed such that the optical beam
focusing means is a slab waveguide provided to guide the diffracted
optical beams and having a parabolic reflecting end face for
reflecting the guided optical beams, and the first photo receiver
is provided at a focal point of the slab waveguide.
The identifier is further constructed such that the optical beam
focusing means comprises a second optical fiber for diffracting the
diffracted optical beams to make the optical beams travel in
cladding mode by using tilted gratings formed in a core portion of
the second optical fiber, and the first photo receiver is provided
at an end face of the second optical fiber to receive the optical
beams traveling in cladding mode within the second optical
fiber.
The identifier is further constructed such that the optical beam
focusing means further comprises a third optical fiber, located
between the optical waveguide and the second optical fiber, for
focusing the diffracted optical beams from the optical waveguide
onto a center of the second optical fiber.
The identifier is further constructed such that the optical
waveguide is provided on a front side of the third optical fiber
and positioned apart a distance two times a focal length of the
third optical fiber for focusing, from the third optical fiber, and
the second optical fiber is provided on a rear side of the third
optical fiber and positioned apart a distance two times a focal
length of the third optical fiber from the third optical fiber.
The identifier further comprises a fourth optical fiber in addition
to the third optical fiber, in which a center of the optical
waveguide is positioned at a front focal point of the third optical
fiber, a center of the second optical fiber is positioned at a rear
focal point of the fourth optical fiber, and the third and fourth
optical fibers focus diffracted optical beams from the optical
waveguide onto the second optical fiber.
The identifier is further constructed such that the optical beam
focusing means is a "f.theta." lens provided so that a central axis
of the core of the optical waveguide and a light receiving face of
the first photo receiver have relationship represented by
"f.theta.", and a tilt angle of each of the plurality of sets of
tilted gratings is determined so that a diffraction direction
associated with diffracted optical beams from each of the plurality
of sets of tilted gratings satisfies relationship represented by
"f.theta.".
The identifier is further constructed such that light-diffracting
efficiency of each of the plurality of sets of tilted gratings is
determined so that intensity of diffracted optical beams from all
of the plurality of sets of tilted gratings becomes uniform by
controlling current supplied to each of the plurality of
grid-shaped electrodes.
An optical router according to the second aspect of the present
invention is for switching between paths for a specific optical
packet out of an optical signal consisting of an optical packet
train having a plurality of optical packets coupled together, and
the optical router comprises: an optical branch for branching the
optical packet train input from an optical transmission input line;
the optical packet header identifier defined in the first aspect of
the present invention for receiving one of optical outputs from the
optical branch; an optical delay device for making the other of
optical outputs from the optical branch delay by a predetermined
time delay; an optical switch for outputting at least one optical
packet having a header identified by the optical packet header
identifier, the optical packet being separated from the optical
packet train output from the optical delay device, to a first
optical transmission output line, and outputting optical packets
excluding the at least one optical packet identified by the optical
packet header identifier to a second optical transmission output
line, based on an output from the optical packet header
identifier.
An optical router according to the third aspect of the present
invention comprises a demultiplexer for demultiplexing the
wavelength-division-multiplexed optical signal input from an
optical transmission input line; a plurality of the optical routers
defined in the second aspect of the present invention for receiving
a plurality of optical outputs having wavelengths different from
one another from the demultiplexer, respectively; and a multiplexer
for multiplexing discrete wavelength optical outputs from the
second optical transmission line of the plurality of the optical
routers defined in the second aspect of the present invention.
An optical router according to the fourth aspect of the present
invention is an optical router having function of Optical Add/Drop
Multiplexer (Optical ADM) for switching between paths for a
specific optical packet out of a plurality of optical packets
coupled together and constituting an optical packet train as an
optical signal and, for inserting an optical packet different from
the specific optical packet into a location of the specific optical
packet, the location becoming empty by switching between paths, and
the optical router comprises: an optical branch for branching the
optical packet train input from a first optical transmission input
line; an optical packet header identifier for receiving one of
optical outputs from the optical branch; an optical delay device
for making the other of optical outputs from the optical branch
delay by a predetermined time delay; and an optical switch for
outputting at least one optical packet having a header identified
by the optical packet header identifier, the optical packet being
separated from the optical packet train output from the optical
delay device, to a first optical transmission output line,
outputting optical packets excluding the at least one optical
packet identified by the optical packet header identifier to a
second optical transmission output line, and inserting an optical
packet from a second optical transmission input line into a
location of the at least one optical packet identified by the
optical packet header identifier, based on an output from the
optical packet header identifier.
An optical router according to the fifth aspect of the present
invention is an optical router having function of Optical Add/Drop
Multiplexer (Optical ADM) for switching between paths for a
specific optical packet out of a plurality of optical packets
coupled together and constituting an optical packet train, and
inserting an optical packet different from the specific optical
packet into a location of the specific optical packet, the location
becoming empty by switching between paths, and the optical router
comprises: a demultiplexer for demultiplexing the
wavelength-division-multiplexed optical signal input from the first
optical transmission input line; a plurality of the optical routers
defined in the fourth aspect of the present invention for receiving
a plurality of optical outputs having wavelengths different from
one another from the demultiplexer, respectively; and a multiplexer
for multiplexing discrete wavelength optical outputs from the
plurality of the optical routers defined in the fourth aspect of
the present invention into a wavelength division multiplexed
optical signal and outputting the multiplexed optical signal to the
second optical transmission output line.
An optical routing method, according to the sixth aspect of the
present invention, using the optical router defined in the fifth
aspect of the present invention, comprises steps of: detecting a
head of the optical packet train based on an output from the second
photo receiver of the optical packet header identifier;
calculating, in the time domain, locations of headers of optical
packets constituting an optical packet train based on the time when
the head of the optical packet train is detected; detecting an
output from the first photo receiver of the optical packet header
identifier at individual times corresponding to the locations; and
making a corresponding optical packet delay by a time period in
order to separate the corresponding optical packet from the optical
packet train input to the optical router, the time period being
equal to a time delay by which the optical packet train is made to
delay by the optical delay circuit to transmit to the optical
switch a control signal so that the optical switch changes its
switch state for a duration of the corresponding optical packet, in
the event the detected output from the first photo receiver is
higher than a predetermined level.
The optical packet header identifier of the present invention
comprises: an optical waveguide configured to have a plurality of
sets of tilted gratings, the locations of which are previously
encoded in a direction along an optical axis, arranged along the
waveguide; light-focusing means; and a photo receiver. Accordingly,
the optical packet header identifier having no necessity for
calculation of correlation between codes performed by an electronic
circuit and a low power consumption, operating at high rate, a
superior reliability, stability and economical efficiency can be
achieved.
Furthermore, the optical packet header identifier of the present
invention can be configured to be programmable as follows. That is,
the optical waveguide comprises a semiconductor optical waveguide,
the plurality of sets of tilted gratings are realized such that a
plurality of sets of grid-shaped electrodes are formed on the
semiconductor optical waveguide and at least one of the plurality
of sets of grid-shaped electrodes is previously selected in
response to a code to be identified, and then is supplied with
current to produce at least one set of tilted gratings within the
semiconductor optical waveguide by utilizing a band-filling
effect.
Moreover, the optical packet header identifier makes it possible to
construct an optical ADM and an optical router each incorporating
the identifier therein and having a simplified configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantage of the present
invention will become apparent from the following detailed
description when taken with the accompanying drawings in which:
FIG. 1 is a diagram illustrating the configuration of a
conventional optical packet header identifier;
FIG. 2 is a diagram illustrating the configuration of a first
embodiment of an optical packet header identifier according to the
present invention;
FIG. 3 is a diagram illustrating the configuration of a first
example of the first embodiment of the optical packet header
identifier according to the present invention and FIG. 3A is a plan
view of the first example of the first embodiment, and FIG. 3B is a
side view thereof;
FIG. 4 is a diagram illustrating the configuration of a second
example of the first embodiment of the optical packet header
identifier according to the present invention and FIG. 4A is a plan
view of the first example of the first embodiment, and FIG. 4B is a
side view thereof;
FIG. 5 is a diagram illustrating the configuration of a third
example of the first embodiment of the optical packet header
identifier according to the present invention;
FIG. 6 is a diagram illustrating the configuration of a fourth
example of the first embodiment of the optical packet header
identifier according to the present invention;
FIG. 7 is a diagram illustrating the configuration of a fifth
example of the first embodiment of the optical packet header
identifier according to the present invention and FIG. 7A is a plan
view of the first example of the first embodiment, and FIG. 7B is a
side view thereof;
FIG. 8 is a diagram illustrating the configuration of a sixth
example of the first embodiment of the optical packet header
identifier according to the present invention and FIG. 8A is a plan
view of the first example of the first embodiment, and FIG. 8B is a
side view thereof;
FIG. 9 is a diagram illustrating the configuration of a second
embodiment of an optical packet header identifier according to the
present invention;
FIG. 10 is a diagram illustrating the configuration of a first
embodiment of an optical network node having the optical packet
header identifier of the present invention applied thereto;
FIG. 11 is a diagram illustrating the configuration of a second
embodiment of the optical network node having the optical packet
header identifier of the present invention applied thereto; and
FIG. 12 is a diagram illustrating the configuration of a third
embodiment of the optical network node having the optical packet
header identifier of the present invention applied thereto.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 is a diagram illustrating the general configuration of an
optical packet header identifier according to the present
invention. The optical packet header identifier comprises an
optical waveguide 10, optical focusing means 15, and photo
receivers 17 and 20, and tilted gratings 11 for diffracting an
incident optical beam 12 to emit the beam as an emitted optical
beam 14 to the outside of the waveguide is formed within the
optical waveguide 10. The tilted gratings are not formed uniformly
along the optical waveguide 10, but are constructed such that a
plurality of sets of tilted gratings are arranged at intervals. The
length of a portion containing a set of tilted gratings and the
length of a portion containing no gratings, can be defined in
increments of length "L." "L" equals to the length that 1-bit in a
digital optical signal 12 occupies within the waveguide 10.
Arrangement of the plurality of sets of tilted gratings along an
optical axis coincides with a previously given address code. As
shown in FIG. 2, an 8-bit code including the binary sequence
"10100101" is provided within the waveguide. The optical signal 12
input to the waveguide travels within the waveguide 10 and at the
moment when arrangement of the code of the optical signal and
arrangement of the plurality of sets of tilted gratings spatially
coincide with one another, the optical beam guided within the
waveguide is diffracted to the outside of the waveguide, while
having its maximum intensity. The optical focusing means 15
performs the spatial integration of the emitted optical beams 14,
which are emitted to the outside of the waveguide by the plurality
of sets of tilted gratings, and then the optical beams 14 are
output as a focused optical beam 16 to the photo receiver 17. When
the photo receiver 17 is made to have a bandwidth so that the
receiver serves as a low-pass filter for making the frequency of a
clock signal input thereto approximately be the cut-off frequency
thereof, the photo receiver 17 performs the integration of the
focused optical beams 16 for a time period, and converts the beam
to an electrical signal, and then outputs an electrical output
signal 18.
The optical packet header identifier outputs a correlation
calculation result 19 as an electrical signal by correlating an
optical signal 13 input to the waveguide and encoded through
intensity modulation with the pattern of the plurality of sets of
tilted gratings that are previously arranged. As shown in FIG. 2,
when arrangement of the optical signal 13 input to the waveguide
and the pattern 11 of the plurality of sets of tilted gratings
coincide with one another, a correlation signal 19 having a high
peak value is output, and when those two components, i.e.,
arrangement and pattern, do not coincide with one another, a peak
does not appear in the signal 19 because of low correlation between
them. The above-described operation makes it possible to detect the
address code added to the optical signal. The photo receiver 20
receives an optical packet train transmitting through the optical
waveguide 10. A photoelectrically converted signal 21 output from
the waveguide is used for producing a timing signal indicative of
locations in headers of individual packets that constitute the
optical packet train to introduce the correlation signal 19, and is
used for producing a timing signal to separate the optical packets,
all of which have the address added thereto.
Assuming that the waveguide is a quartz waveguide containing Ge and
has a refractive index of 1.45, and the wavelength of optical
signal is 1.55 .mu.m, and further a bit rate is 40 Gbps, the length
"L" along the waveguide, which length corresponds to 1-bit in an
optical signal, is 2.6 mm, and the length that corresponds to 8-bit
in a signal is about 21 mm. The tilted gratings are formed to have
a periodic interval of 0.76 .mu.m, provided that the gratings
diffract the incident optical beam 12 in a direction vertical to an
optical axis, and then produce the emitted light 14. In case of a
fiber Bragg reflector for optical communication, gratings are
formed therein for practical use to have a periodic interval of
about 0.5 .mu.m. Therefore, the previously described gratings can
be formed using a well-known technique for forming a fiber grating
through interference generated, using a phase grating, between
optical beams having a short wavelength, such as KrF excimer
excitation light.
When the waveguide is a semiconductor with a refractive index of
3.5, the length that 8-bit in a signal occupies within the
waveguide can further be shortened to 8.7 mm, and the tilted
gratings can be formed to have a periodic interval of 0.3 .mu.m,
meaning that a desired waveguide can easily be fabricated by a
lithography technique.
A detailed embodiment of the above-described optical packet header
identifier and examples describing the embodiment in more detail
will be disclosed below. In a first embodiment, the optical
waveguide 10 depicted in the general diagram of the present
invention shown in FIG. 2 comprises an optical fiber, and the
optical focusing means 15 is realized by the following examples 1
through 6. Though not shown, the configurations of the examples all
include the photo receiver 20.
FIG. 3 illustrates a first example showing an optical packet header
identifier comprising a single-mode optical fiber 110 for
communication, a planar slab waveguide 115 having a reflecting
plane, whose outline is parabolic, in a plane thereof and a photo
receiver located at a focal point P on a parabolic curve, and FIG.
3A is a plan view of the identifier, and further, FIG. 3B is a side
view thereof. In a core of the optical fiber 110, tilted gratings
111 are formed such that locations of the plurality of sets of
tilted gratings along an optical axis are encoded.
When an incident optical beam 12 having an address added thereto
through intensity modulation travels within the optical fiber, the
beam is diffracted by the tilted gratings in a direction
approximately vertical to the optical axis of the core. The
diffracted optical beams are incident on the slab waveguide 115,
and travel while being totally reflected by both the primary
principal surfaces of the waveguide, and then, are focused onto a
focal point "P" as is seen when using a parabolic antenna because a
plane of the waveguide facing the incident plane thereof has a
parabolic reflecting surface, and further the spatial integration
of the focused optical beams is performed. Disposed at the focal
point "P" is a photo receiver 17 for outputting a correlation
signal as an electrical output signal 18 indicative of a
correlation between the address code added to an optical signal and
the spatially-encoded arrangement of the plurality of sets of
tilted gratings by using ability of photo receiver to perform time
integration and photoelectric conversion function thereof.
Thickness of the slab waveguide may be determined such that a
diffracted optical beam leaving the core of the optical fiber and
expanding in a direction vertical to the plane of this figure can
entirely be captured by the slab waveguide when the beam reaches
the end face of the slab waveguide. Since an optical beam is guided
nearly exhibiting a Gaussian distribution within an optical fiber,
the thickness T of the slab waveguide may be represented by
relationship:
where: "z" is a distance in air from the core to the linear side
face of the slab waveguide; "2w" is a beam size (entire width) at
the distance "z"; "2w.sub.0 " is a beam size (entire width) when
the beam propagates in the single-mode optical fiber 110; and
".lambda." is a wavelength. When wavelength is 1.55 .mu.m and the
side face of the optical fiber and the linear side face of the slab
waveguide contact one another, and further when taking into account
the assumption that "2w.sub.0 " is about 6 .mu.m in case of the
single-mode fiber, the beam size "2w" at the end face of the slab
waveguide on which optical beams are incident is about 30 .mu.m,
and accordingly the waveguide may need to have a thickness in the
range from 30 to 50 .mu.m.
Furthermore, a reflective coating material may be applied to the
parabolic plane if necessary, or selecting a parabolic function of
the parabolic plane also makes it possible for all of optical beams
to totally be reflected on the parabolic plane.
FIG. 4 illustrates a detailed second example of the optical packet
header identifier according to the present invention. The
identifier of the second example comprises a single-mode optical
fiber 110 in which a plurality of sets of tilted gratings 111 are
formed such that locations of the plurality of sets of tilted
gratings are encoded along an optical axis, a multi-mode optical
fiber 310 in which tilted gratings 311 are formed uniformly within
the core of the fiber along an optical axis, a focusing optical
fiber 210 serving as a cylindrical lens for focusing diffracted and
emitted optical beams from the plurality of sets of tilted gratings
111 of the single-mode optical fiber 110 onto the core of the
multi-mode optical fiber 310, and a photo receiver 17 located at
the output end of the multi-mode optical fiber 310. FIG. 4A is a
plan view of the identifier, and FIG. 4B is a side view thereof. It
should be appreciated that the example employs the focusing optical
fiber 210 and the multi-mode optical fiber 310 instead of the
optical focusing means 15 shown in FIG. 2.
The tilted gratings 311 of the multi-mode optical fiber 310 are
configured to make optical beams focused through and input from the
focusing optical fiber 210 diffracted to travel in cladding mode
within the multi-mode optical fiber 310. In more detail, the
optical fibers 110 and 310 are made of the same material, and
different only in the core diameter. The plurality of sets of
tilted gratings 111, the locations of which are encoded within the
fiber to correspond to an address code, and the tilted gratings 311
formed uniformly within the core of the fiber each have gratings
formed at the same periodic intervals and tilted at angles slightly
different from one another. The plurality offsets of tilted
gratings 111 are configured to have gratings tilted at a specific
angle relative to the optical axis of the core in order to diffract
an optical beam guided along the fiber in a direction approximately
vertical to the optical axis. The tilted gratings 311 uniformly
formed along the core of the fiber 310 are configured to have
gratings tilted at a specific angle relative to the optical axis of
core in order to diffract optical beams incident vertically thereon
not in parallel with the optical axis of core, but at an angle
slightly distorted such that the optical beams travel in cladding
mode within the optical fiber 310 after being diffracted. This is
because when optical beams are diffracted in parallel with the
optical axis of core, the beams are re-diffracted within the tilted
gratings 311. In the optical fiber 310, the cross section of clad
is far larger than that of the core, and therefore optical beams
traveling in cladding mode within the fiber are less re-diffracted
by gratings formed in the core. This allows optical beams traveling
in cladding mode to propagate within the cladding of the optical
fiber 310 without experiencing any transmission losses due to the
uniformly formed gratings 311, and transfer their entire power to
the photo receiver provided at the output end.
The focusing optical fiber 210 serving as a cylindrical lens is
disposed such that the cores of the optical fibers 110 and 310 are
positioned respectively at locations apart a distance in air two
times focal length from the principal plane of the fiber 210, in
order to couple optical beams in the same optical magnification.
Focal length "f" of the cylindrical lens having a refractive index
"n" and an entire circle of radius "r" is represented by the
following equation.
When the focusing optical fiber 210 is realized by employing a
silica optical fiber that has a refractive index of 1.45 and a
diameter "2r" of 125 .mu.m, "f" becomes equal to 1.61r and thereby,
is 100.6 .mu.m. Accordingly, the optical fibers 110, 310 and the
focusing optical fiber 210 may be disposed such that spacing
between centers of the cores of the optical fiber 110 and the
focusing optical fiber 210, and spacing between centers of the
cores of the optical fiber 310 and the focusing optical fiber 210
each become 201.2 .mu.m in air.
In the above-described second example, although the focusing
optical fiber 210 is optically disposed so that the beams emitted
from the optical fiber 110 are focused onto the optical fiber 310
in the same optical magnification, optical fibers 410-1 and 410-2
may be employed as two cylindrical lens, as shown in a third
example depicted in FIG. 5, in which emitted optical beams from the
fiber 110 are once made to be collimated optical beams in a plane
vertical to the paper by the first optical fiber, and then the
collimated optical beams are focused through the second optical
fiber, thereby constituting an optical infinite arrangement.
Moreover, as shown in a fourth example depicted in FIG. 6, the
identifier of the invention may be constructed such that the
focusing optical fiber 210 is omitted and cylindrical faces of the
optical fiber 110 for diffraction of light and the optical fiber
310 for reception of light are disposed near one another, and as a
result, the slab waveguide of the first example having a parabolic
reflecting end face is replaced by the optical fiber 310 for
reception of light.
Location at which the optical fiber 310 for reception of light is
to be disposed and core diameter that the optical fiber 310 for
reception of light is to have for receiving all of diffracted
optical beams from the optical fiber 110 will be calculated. The
calculation can be performed by using a focusing formula applied to
the case where optical beams are focused through one of side faces
of the optical fiber 310 for reception of light. A distance "d"
between center of the core of the optical fiber 110 for diffraction
of light and cylindrical face of the optical fiber 310 for
reception of light, which distance is determined such that
diffracted optical beams from the optical fiber 110 for diffraction
of light travel the distance "d" and after traveling through the
curved face of the optical fiber 310 for reception of light, are
collimated within the optical fiber 310 for reception of light,
becomes about 140 .mu.m in air. When making a distance between the
two fibers larger than this value, the diffracted optical beams are
focused within the optical fiber 310. When the distance "d" is
determined so that the diffracted optical beams from the optical
fiber 110 collimated within the optical fiber 310, a height 2w of
the diffracted optical beams from the optical fiber 110 for
diffraction of light becomes about 45 .mu.m at the side face of the
optical fiber 310, provided that the optical beams within the core
of the optical fiber 110 for diffraction of light nearly are
Gaussian beams having a diameter of 2w.sub.0 =6 .mu.m. Accordingly,
the core of the optical fiber 310 for reception of light may have a
diameter of about 50 .mu.m.
An advantage of the example is that, even when bit rate of optical
signal is low and/or length of address code becomes long, the
element never becomes longitudinally large in size. For example,
when the bit rate of signal is 1 Gbps and the address code has 32
bits in length, the optical fibers 110, 310 disposed near one
another should have a long length of 3.2 m. However, the optical
fibers 110, 310 having such long length can be mounted in a small
space by winding the two fibers in the form of a coil or reel.
Furthermore, the above-described bit rate of signal corresponds to
the bit rate used in LAN such as Ethernet (registered trademark) or
an access system. This means that the present invention can
effectively be used even at a bit rate of signal at which a
terminal located at the termination of network operates.
A fifth example is illustrated in FIG. 7. FIG. 7A is a plan view
and FIG. 7B is a cross sectional view taken along a central line of
the plan view.
The optical packet header identifier of the example comprises an
optical waveguide 510 having a circular optical axis, a cylindrical
lens 520 depicted as a circular arc in the same plane as the
optical waveguide 510, a normal focusing lens 530 having
axisymmetric focusing power, and a photo receiver 17. It should be
appreciated that the example employs the cylindrical lens 520 and
the focusing lens 530 instead of the focusing means 15 shown in
FIG. 2.
The optical waveguide 510 has a plurality of sets of tilted
gratings 511 provided in a core thereof such that the locations of
the plurality of sets of tilted gratings 511 are encoded along the
optical axis within the waveguide. Each set of tilted gratings 511
are tilted at an angle such that a central axis of diffracted
optical beams emitted from the each set of tilted gratings passes
through a point Q shown in the plan view of FIG. 7A. As shown in
FIG. 7B, which is the cross section cut by a plane vertical to the
paper, the cylindrical lens 520 is disposed to have its focal point
at the center of the core of the optical waveguide 510 in order to
collimate optical beams emitted from the tilted gratings and
expanding therefrom, within the cylindrical lens 520. Furthermore,
the cylindrical lens 520 is depicted as a circular arc centering
the point "Q" so as not to cause optical aberration in the
collimated optical beams emitted from each of the plurality of sets
of tilted gratings 511. The focusing lens 530 having axisymmetric
focusing power focuses an image formed at the point "Q" onto the
photo receiver 17.
A sixth example is illustrated in FIG. 8. FIG. 8A is a plan view
and FIG. 8B is a cross sectional view taken along a central line of
the plan view.
The optical packet header identifier of the example comprises a
linear-shaped optical waveguide 110, a focusing lens 630 having
different lens characteristics in a horizontal plane and a plane
vertical to the horizontal plane, and a photo receiver 17. The
example employs only the focusing lens 630 instead of the focusing
means 15 shown in FIG. 1.
The optical waveguide 110 has a plurality of sets of tilted
gratings 611 provided in a core thereof so that the locations of
the plurality of sets of tilted gratings are encoded along the
optical axis within the waveguide. Each of the plurality of sets of
tilted gratings 511 are tilted at an angle such that a distance "t"
from a central position "R" of the optical axis of optical fiber to
a central position of each of the plurality of sets of tilted
gratings in a longitudinal direction and an angle ".theta." at
which an optical beam incident on the waveguide is diffracted by
the corresponding set of tilted gratings satisfy the relationship
represented by t=f.theta.. In this case, "f" represents a focal
length within a horizontal plane of the focusing lens 630.
The focusing lens 630 acts as a "f.theta." lens within the
horizontal plane and as a cylindrical lens to focus optical beams
emitted and expanding from the plurality of sets of tilted gratings
611 within the core of the optical waveguide 110, onto the photo
receiver 17 within the vertical plane. A lens performing different
lens operations in planes orthogonal to one another can be realized
by, for example, employing a composite lens composed of an
"f.theta." lens and a cylindrical lens, a hologram lens, an
aspherical lens, etc. Furthermore, instead of lens, an aspherical
mirror may be employed.
Although in the embodiments described so far, as the optical fibers
110, 510 each have a plurality of sets of tilted gratings provided
therein so that the locations of the plurality set of tilted
gratings are encoded, a single-mode optical fibers for
communication are employed, but the embodiments need not to be
limited to employment of single-mode optical fiber, but may employ
a multi-mode optical fiber.
Moreover, material of fiber employed in the invention is not
limited to a silica, but may be a glass or plastic. Additionally,
the core employed in the invention is not limited to a circular
core, but may be a rectangular core or a channel optical waveguide
formed on a planar substrate.
In addition, the focusing means employed in the invention is not
limited to an optical fiber and a planar waveguide, and further,
material of the focusing means is not limited to a glass and
plastic.
To make a correlation signal output from the photo'receiver 17
shown in FIG. 2 output a clear correlation peak that has a
symmetrical waveform and exhibits no deformation of waveform in the
time domain, intensities of diffracted optical beams from all the
tilted gratings 11 need to be uniform. When the intensities of
diffracted optical beams along the optical axis of the optical
waveguide 10 are significantly differed, the waveform of
correlation signal deforms and then a peak indicative of clear
correlation may not appear. When diffraction efficiency of the
plurality of sets of tilted gratings is low, the amount of optical
power attenuated in proportion to a distance that the incident
optical beam 12 propagates along the optical axis of the optical
waveguide 10 is small, and diffracted optical beams from any one of
the plurality of sets of tilted gratings are output, having
approximately equal intensity.
In the event the above-described diffraction efficiency is made
relatively high to increase the quantity of light to be received by
the photo receiver 17, the previously mentioned fault will occur.
If the diffraction efficiency is made different depending on the
locations of the plurality of sets of tilted gratings, the fault
can be avoided. In more detail, a desired optical waveguide is
constructed such that diffraction efficiency of sets of tilted
gratings located near the input end of the waveguide for an
incoming optical beam is made low and diffraction efficiency of
sets of tilted gratings located near the output end thereof for an
outgoing optical beam is made high, thereby allowing intensity of
diffracted optical beams from any one of the plurality of sets of
tilted gratings to substantially be the same. The above-described
desired optical waveguide can be realized by controlling intensity
of ultraviolet ray (UV ray) to be irradiated, the number of pulses
in UV ray, and/or time period over which UV ray is being
irradiated, at the time of formation of fiber grating.
Furthermore, in the second to fourth examples, each employing as an
optical focusing member an optical fiber for reception of light in
which gratings are formed, the optical fiber 310 for reception of
light may be made to have weighed diffraction efficiency along the
optical axis, or the optical waveguide may be made together with
the optical fiber 310.
A second embodiment of the optical packet header identifier
according to the present invention will be explained below. Based
on the concept shown in FIG. 2, the second embodiment employs a
semiconductor optical waveguide as the optical waveguide 10, and
realizes gratings by forming in the semiconductor optical waveguide
spatial periodicity of refractive index variation, which
periodicity is generated so that refractive index within the
waveguide is lowered by performing spatial periodic current
injection (carrier injection) into the waveguide so that the
injection acts through a band-filling effect on a guided optical
beam. The band-filling effect means a phenomenon in which empty
energy levels within an energy band are filled by injecting of free
carriers to shift wavelength at absorbance edge substantially to
the side of short-wavelength, thereby lowering refractive index of
semiconductor, as is known to those skilled in the art. The
lowering of refractive index is independent on polarized wave.
Focusing means and two photo receivers of the embodiment are
configured to have the configuration similar to that of the first
embodiment.
FIG. 9 illustrates an optical waveguide which is constructed such
that buried-channel optical waveguide of "p-i-n" structure is
formed through etching and growth of crystalline on a transparent
semiconductor substrate and a plurality of sets of electrodes are
disposed thereon in the form of duckboard, and forward current is
injected between selected set of electrodes and a ground electrode
located on a back face of the substrate. Formed within channel
waveguide below selected duckboard-shaped set of electrodes are
periodic refractive index gratings through the above-described
band-filling effect. The periodic refractive index gratings are not
formed below unselected set of electrodes. The concept of the
present invention shown in FIG. 2 is realized by selecting sets of
electrodes to be conducted current so that the selected sets of
electrodes corresponds to an address code. This indicates that the
second embodiment has a significant advantage over the first
embodiment in that although a code produced by corresponding sets
of tilted gratings is fixed in the first embodiment, a code
produced by the same is programmable in the second embodiment.
A semiconductor optical waveguide 710 having programmable chirp
gratings therein is formed such that an n-type cladding layer 713,
an i-layer 714 as a core, a p-type cladding layer 715 and a p-type
contact layer 716 on a n-type semiconductor substrate are laminated
through crystal growth technique in a planar form and both sides of
the laminated layers are etched to expose the substrate so that the
remaining laminated layers become a channel waveguide, and the
channel waveguide is buried in the optical waveguide by filling
both sides of the channel waveguide with an insulative component
717 having a low carrier concentration. Thereafter, a plurality of
sets of duckboard-shaped electrodes 711-1 to 711-5 are formed on
the waveguide, and a ground electrode 719 is formed over the back
face of the substrate. Two sets of duckboard-shaped electrodes
adjacent to one another are electrically isolated from one another.
Spacing between grids formed within each of the plurality of sets
of duckboard-shaped electrodes and an angle at which a guided
optical beam propagates relative to an optical axis are determined
such that refractive index gratings formed within the optical
waveguide by conducting current between a set of electrodes and the
back face electrode 719 diffract an incident optical beam 718 in a
direction approximately orthogonal to the waveguide to produce
diffracted optical beams 14.
Length "L" of one set of duckboard-shaped electrodes along the
optical axis is determined to be equal to the length that 1-bit of
a signal in the incident optical beam 718 within the semiconductor
crystalline. Sets of electrodes to be conducted current are
selected based on an address code in the header portion of an
optical signal to be detected. In FIG. 9, the address code is
represented by a 5-bit code including the binary sequence "10010",
and the sets of electrodes 711-1 and 711-4 are selected
correspondingly. That is, refractive index gratings are formed only
below the two sets of electrodes 711-1 and 711-4 through a
band-filling effect.
By combining the semiconductor optical waveguide 710, the optical
focusing member 15 having detailed configuration shown in the
above-described examples 1 through 7, and the photo-receiver 17
together, only when an incoming optical packet 718 has a header
code, including the binary sequence "10010," added thereto, the
correlation signal shown in FIG. 2 is output from the photo
receiver 17. As is described above, since the second embodiment has
ability to optionally select sets (or a set) of electrodes to be
conducted current, a header code to be identified can optionally be
determined, whereby a programmable optical packet header identifier
can be constructed.
Additionally, adjusting the amount of current to be supplied to
corresponding sets of electrodes easily allows intensity of
diffracted optical beams to be uniform along an optical axis.
It should be appreciated that an optical semiconductor material to
be employed can be realized by selecting a most effective material,
such as Si series, InP series, GaAs series and AlN series,
depending on the wavelength of an optical signal to be used.
An embodiment of an optical network incorporating therein the
optical packet header identifier of the present invention will be
disclosed below.
FIG. 10 is a diagram illustrating the configuration of an Optical
Add/Drop Multiplexer (OADM) that incorporates therein the optical
packet header identifier of the present invention. An OADM 800
comprises an optical packet header identifier 801 of the present
invention, a 2.times.2 optical switch circuit 802, an optical
switch control circuit 803, an optical branch 804, and an optical
delay circuit 805.
An incident optical signal 806 coupling a number of packets
together and input to the OADM 800 is branched into two signals by
the optical branch 804, and then one of the two signals is input to
the optical packet header identifier 801, whether the other is
delayed by the optical delay circuit 805, thereby being input to
the 2.times.2 optical switch circuit 802. The optical packet header
identifier 801 calculates correlation between an address code
previously given to the identifier and an optical packet input to
the identifier, and then outputs a correlation signal 818 having
the waveform 19 shown in FIG. 2 and a signal 821 produced by
converting an optical packet signal which transmits through the
optical waveguide 11 shown in FIG. 2 to an electrical signal.
The optical switch control circuit 803 detects a head of an optical
packet train from the photoelectrically converted packet signal
821. Locations in the time domain at which the headers of
individual packets are located are identified based on the time
when the head of the packet train has been detected, time windows
are periodically created, and then the correlation signal 818 is
captured at individual times corresponding to the time windows.
Upon detection of the correlation signals, in order to separate all
the packets, whose correlation signals were detected, from the
packet train input to the identifier, the optical switch control
circuit 803 outputs a control signal 815 to the 2.times.2 optical
switch circuit 802, so that the 2.times.2 optical switch circuit
802, which is normally in a pass-through switch state, is delayed
by the time delay by which the corresponding packets are delayed by
the optical delay circuit 805, and changes its state, and then
stays in a cross switch state for the duration of the corresponding
packet. This allows only the packets, which are to be separated
through the OADM 800 at this node and from an optical packet train
809 passing through the optical delay circuit 805, to be output to
a separation output 810, and the remainder of the packet train is
output to a transmission output line 812 after passing through the
OADM because the 2.times.2 optical switch circuit 802 is in a
pass-through switch state. When another packet is inserted through
this node into an empty time slot, in which the corresponding
separated packet was located, a packet to be inserted is input from
an input port 811, creates a new optical packet train along with
other packets, which were input through the input 806 and not
separated at this node, and finally, is output to the transmission
output line 812.
In the case where the separation output 810 does not terminate at
this node, but is transmitted to a transmission output line
different from the transmission output line 812, the node 800 comes
to operate as a router.
The 2.times.2 optical switch circuit 802 that operates at high rate
may be a waveguide optical switch that uses lithium niobate
crystalline having a ferroelectric crystalline. In addition, the
optical delay circuit 805 may be an optical fiber delay line.
FIG. 11 illustrates an embodiment in which an Optical Add/Drop
Multiplexer (OADM) node in a Wavelength-Division Multiplexing (WDM)
transmission system is constructed by employing the optical packet
header identifier of the present invention.
A WDM-OADM comprises a demultiplexer 901 for demultiplexing
wavelength division multiplexed (WDM) optical signals input from a
primary transmission line 906, a plurality of OADMs 800-1 to 800-n
which are provided such that n pieces of the OADMs shown in FIG. 9
are arranged in parallel with one another so as to correspond to
individual wavelengths, and a multiplexer 902 for multiplexing
optical signals passing through the OADMs and a packet newly
inserted at this node to create a new packet train, and for
transmitting the new packet train to a primary transmission line on
the side of output. How an OADM operates is the same as that
explained in the description of FIG. 10.
In the embodiment, in order for the WDM-OADM to be able to securely
multiplex and demultiplex optical signals even when optical signals
having different wavelengths are not in synchronization with one
another in the time domain, the OADMs corresponding to individual
wavelengths each include the optical packet header identifier of
the present invention.
The optical packet header identifier 801 is configured to detect
one address code in the above-stated explanation. However, in order
for the optical packet header identifier to be able to detect
different multiple address codes, the optical waveguide 10
constituting the optical packet header identifier may be configured
to have a plurality of waveguides connected in series, so that each
of the plurality of waveguides contains a plurality of sets of
tilted gratings, the locations of which are encoded in accordance
with a code different from other codes.
Furthermore, in the case where a separation output from each of the
OADMs 800-1 to 800-n does not terminate at this node, but is
transmitted to a transmission output line different from the
transmission output line 912 after being multiplexed, the node 800
comes to operate as a router.
FIG. 12 illustrates the configuration of WDM-OADM in which
wavelength-multiplexed optical packet trains are in synchronization
with one another in the time domain, and packet length of each of
packets that constitute a packet train is the same. In this case,
individual OADMs corresponding to individual wavelengths need not
to have the optical packet header identifier provided therein, but
can share one optical packet header identifier.
The WDM-OADM of the embodiment comprises an optical branch 804 for
branching all together optical signals inserted into and
transmitted through the primary optical transmission line 906, and
corresponding to a number of wavelengths, an optical packet header
identifier 801 to which one of the branched optical beams is input,
and further which is constructed by coupling in series optical
packet header identifiers corresponding to different wavelengths,
an optical delay circuit 805 by which the other of the branched
optical beams is delayed, an optical demultiplexer 901 for
demutiplexing wavelength division multiplexed optical signals
passing through the optical delay circuit 805, a 2.times.2 optical
switch circuit 802 to which each of demultiplexed optical signals
corresponding to individual wavelengths is input, an optical
multiplexer 902 for multiplexing discrete wavelength optical beams
output from the 2.times.2 optical switch circuit 802, and
transmitting the multiplexed beams to a primary transmission output
line 912, and an optical switch control circuit 813.
Optical packet header identifiers 801-1 to 801-n are constructed
such that the optical waveguide 10 shown in FIG. 2 constitutes a
plurality of optical waveguides, which are coupled in series along
an optical axis and each of the plurality of optical waveguides has
a plurality of sets of tilted gratings arranged therein, encoded to
correspond to an associated code, and corresponding to a wavelength
different from the remaining wavelengths, and in addition, are
provided means for focusing and receiving individual diffracted
optical beams corresponding to different wavelengths. The photo
receiver 20 shown in FIG. 2 is singly employed in the embodiment
for receiving a packet train that contains optical beams
corresponding to a plurality of wavelengths and packets provided in
the same format and being in synchronization with one another.
Although operation of the WDM-OADM of the embodiment is similar to
that explained in the description of the embodiment shown in FIG.
10, the optical switch control circuit 813 transmits a control
signal for opening/closing switch to a plurality of 2.times.2
optical switch circuits 802-1 to 802-n.
The embodiment also detects a plurality of address codes using one
wavelength, and then separates corresponding packets (or a
corresponding packet). This operation is similar to that explained
in the description of the embodiment shown in FIG. 11.
Furthermore, in the case where a separation output from each of the
2.times.2 optical switch circuits 802-1 to 802-n does not terminate
at this node, but is transmitted to a transmission output line
different from the transmission output line 912 after being
multiplexed, the node 800 comes to operate as a router.
As described so far, although an optical ADM has been described as
an example of an optical network node that employs the optical
packet header identifier of the present invention, instead of
optical ADM, an Optical Cross Connect (OXC) may be also employed.
The special packet header identifier of the present invention can
be used in a system for routing optical packets over a wide area
while maintaining the packets in the form of light.
While the present invention has been described in connection with
certain preferred embodiments, it is to be understood that the
subject matter encompassed by the present invention is not limited
to those specific embodiments. On the contrary, it is intended to
include all alternatives, modifications, and equivalents as can be
included within the spirit and scope of the following claims.
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